Self- vs. Cross-Pollination
A major advantage of self-pollination is its certainty. Continued self-pollination over many generations, however, results in weaker progeny. This is considered to like inbreeding depression. From the evolutionary point of view, self-pollination is a disadvantage as 'there is no scope of genetic recombination. Cross-pollination brings pollen grains from other plants which are genetically different. Genetic heterogeneity is advantageous for the plant in many respects.
The offspring are more vigorous and better adapted for survival even under adverse environmental conditions. Thus cross-pollinated species show wider distribution when compared to self- pollinated species. Thus cross-pollination is favorable for evolution. The main disadvantage of cross-pollination is its uncertainty. It also involves considerable expenditure of resources by the plants as they have to produce an enormous amount of pollen, as compared to self-pollinated plants, to compensate for wastage. Further, when the pollinating agent is an animal, the plant should also provide adequate rewards for the pollinating agent in the form of pollen or nectar.